Stereoselective synthesis of 2-substituted 3-azabicyclo[3.2.0]heptan-2-ones by [2+2]-cycloaddition of N-allyl-β-N-keteniminium salts derived from (R)-vinylglycinol

A stereoselective synthesis of (1R,2R,5S)-2-benzyloxymethyl-3-azabicyclo[3.2.0]heptan-2-one was achieved, by intramolecular [2+2]-cycloaddition of (R)-vinylglycinol-derived N-allyl-β-N-keteniminium salts, with high facial diastereoselection. The regio- and stereochemical courses have been qualitatively investigated by Molecular Mechanics calculations.     

Aza- and carbo-[3+3] annulations of exo-cyclic vinylogous amides and urethanes. Synthesis of tetrahydroindolizidines and an unexpected formation of hexahydroquinolines

[3+3] Annulations of exo-cyclic vinylogous amides and urethanes with vinyl iminium salts are described here. We observed an intriguing dichotomy in their reaction pathways. For pyrrolidine- and azepane-based vinylogous amides or urethanes, aza-[3+3] annulation would dominate to give tetrahydroindolizidines, whereas, unexpectedly, for piperidine-based vinylogous amides or urethanes, carbo-[3+3] annulation was the pathway, leading to hexahydroquinolines. The origin for such a contrast is likely associated with a switch in the initial reaction pathway between C-1,2-addition and C-1,4-addition.     

An efficient synthesis of 2-isoxazolines from α-haloketone oximes and dimethyl sulfonium salts

2-Isoxazolines were synthesized efficiently from a formal [4+1] cycloaddition of nitrosoalkenes and sulfur ylides, which were generated in situ from α-haloketone oximes and dimethyl sulfonium salts. This approach provides a new method to synthesize a range of 2-isoxazolines in high yields and high regioselectivity.     

Convenient synthesis of pyrazolo[3,4-b]pyridin-3-ones and pyrazolo[3,4-b]pyridine-5-carbaldehyde using vinamidinium salts

An expedient method for the synthesis of 2-phenyl-5-aryl-2,3-dihydropyrazolo[3,4-b]pyridin-3-ones and 2-phenyl-3-oxo-2,3-dihydropyrazolo[3,4-b]pyridine-5-carbaldehyde in a single-step via condensation of vinamidinium salts with 3-amino-1-phenyl-2-pyrazolin-5-one is described.     

Synthesis of new derivatives of 1,5,9,13-tetraaza[16]annulene using 2-substituted vinamidinium salts

New 7,15-dibromo-, 7,15-di(bromomethyl)-, and 7,15-di[4-(bromomethyl)phenyl]-1,5,9,13-tetraaza[16]annulene derivatives are synthesized via the condensation reaction of 2-substituted vinamidinium salts [2-substituted 3-(dimethylamino)-N,N-dimethyl-2-propen-1-aminium salts] with 1,8-diaminonaphthalene in acetonitrile/acetic acid. The ultraviolet spectral behavior of these compounds is examined in DMSO.     

Effects of electrolytes on the configuration change of cobalt(II)-halide complexes in chloroform/water reverse micelle systems.

The effects of various salts and HClO4 on the configuration change of cobalt(II)-halide complexes in CHCl3/CTAC or CTAB/H2O reverse micelle systems were examined at 25 degrees C by means of spectrophotometry, where CTAC and CTAB represent cetyltrimethylammonium chloride and bromide, respectively. The formation of the [CoCl4]> or [CoBr4]2- species of the tetrahedral configuration from [Co(H2O)6]2+ of the octahedral configuration in the reverse micelles was greatly promoted not only by a decrease in the W value (W = [H2O]/[surfactant]), but also, at a constant W value (e.g., W = 2.0), by the addition of relatively low concentrations of salts or the acid (e.g., 4.0 mol dm(-3) in the aqueous phase or 4.0 x 10(-2) mol dm(-3) in the whole reverse micelle system). The effects of perchlorate salts increased as Na+ < or = Li+ approximately H+ < Sr2+ < Ca2+ < Mg2+. Non-metallic salts, various tetraalkylammonium (R4N+) salts at lower concentrations, gave minor effects. The enhanced effects of metal salts on the configuration change of the cobalt(II)-halide complexes were interpreted by a further distortion of the hydrogen-bonded structure of the water in a "water pool" in the presence of salts of even relatively low concentrations. A conformation change with increasing temperature was also attributed to a further distortion of the water structure. An almost completed formation of [CoBr4]2- as well as [CoCl4]2- was attained in the reverse micelles at a low W value of 0.69 containing LiClO4 or HClO4. A partial transfer of the [CoX4]2- species from a "water pool" into the CHCl3 phase by the addition of the metal salts may be suspected. An examination of cobalt(II)-bromide complexes in dichloromethane/CTAB/H2O at W = 1.3 - 5.55 justified all the arguments concerning the chloroform systems. The Raman spectra of D2O containing concentrated LiBr and LiClO4 have supplied conclusive evidence that the hydrogen-bonded structure of the bulk water is completely distorted by extremely concentrated salts.     

First acetylenic derivatives of stable 3-imidazoline nitroxides

The Stephens-Castro reaction of copper(I) salts of 1-aryl(hetaryl)alkynes with 2,2,5,5-tetramethyl-4-[2-(4-iodophenyl)-vinyl]imidazoline-3-oxide-1-ol proved to be a general method for the preparation of 2,2,5,5-tetramethyl-4-[2-(p-aryl(hetaryl)ethynylphenyl)]vinyl-3-imidazoline-3-oxide-1-oxyles.     

Identification of [1,3]dithiolo[4,5-d]dithiazolyl radicals by in situ EPR spectroscopy and cyclic voltammetry

The synthesis of [1,3]dithiolo[4,5-d]dithiazolium salts from readily available zinc chelate has been developed. Chlorination of 2-oxo and 2-(dicyanomethylene) (2-oxo-1,3-dithiole-4,5-diyl) diethanethioates with SO₂Cl₂ followed by condensation with Me₃SiN₃ produced 1,2,3-dithiazolium chlorides. The structure of 5-(dicyanomethylene)[1,3]dithiolo[4,5-d][1,3,2]dithiazol-1-ium tetrafluoroborate was confirmed by powder X-ray diffraction, and its chemical bonding pattern as well as charge transfer were studied within the QTAIM framework applied to the results of plane wave DFT periodic calculations. Reduction with triphenylantimony and electrochemical reduction of [1,3]dithiolo[4,5-d]dithiazolium salts by cyclic voltammetry, chronoamperometry, and microelectrolysis at a controlled potential on a platinum electrode in acetonitrile revealed the formation of [1,3]dithiolo[4,5-d]dithiazolyl radicals, which were characterized by EPR spectroscopy.     

Cycloaddition of keteniminium with terminal alkynes toward cyclobuteniminium and their use in Diels–Alder reactions

An efficient access to cyclobutanone derivatives has been developed via a ‘one-pot’ [2+2]/[4+2] sequence involving keteniminium and cyclobuteniminium salts as key intermediates. A broad range of novel cyclobuteniminium salts have been prepared via [2+2] cycloaddition of keteniminium salts and alkynes. The resulting [2+2] adducts were then further transformed by Diels–Alder reaction with various dienes to afford cyclobutanone derivatives in good yields. A density functional theory (DFT) based computational study has been performed to obtain insight into the nature of the cycloaddition reactions and to investigate the difference in reactivity of cyclobuteniminium salts. Finally, the usefulness of cyclobutanone derivatives has been demonstrated by ring expansion reactions affording lactone, lactame, and cyclopentanone derivatives.     

Synthetic procedure to pyrido[2,1-f][1,2,4]triazinium salt and related compounds

N-aminopyridyl ketone salts were reacted with formamide to yield heteroaromatic pyrido[2,1-f][1,2,4]triazinium salts. Upon storage of these products in the presence of water, formation of covalent hydrates have been observed. Reaction of the same starting compound with urethane yielded 3-chloropyrido[2,1-f][1,2,4]triazinium salt which readily reacted with secondary amines to afford 3-amino derivatives. An analogous ring closure reaction of 2-formylaminomethyl- and formaminobenzylpyridine allowed the synthesis of the partially reduced 3,4-dihydropyrido[2,1-f][1,2,4]triazinium compounds. The cyclization procedure was also applied for the synthesis of the related pyrimido[2,1-f][1,2,4]triazinium salt.     

New heterocyclic sym-triazolopyrimidinium systems — Quinoline,pyridazine, and phthalazine derivatives

Pyrimido[1′,2′:1,5]-sym-triazolo[4,3-b]pyridazinium, pyrimido[1′,2′:1,5]-sym-triazolo-[4,3-b]phthalazinium, and pyrimido[1′,2′:1,5]-sym-triazolo[4,3-a]quinoliniumsalt derivatives were obtained by condensation of 3-amino-sym-triazolo[4,3-b]pyridazinium, 3-amino-sym-triazolo[3,4-a]phthalazinium, and 1-amino-sym-triazolo[4,3-a]quinolinium salts with β-diketories and 1,1,3,3-tetraethoxypropane. The structures of the reaction products were confirmed by the P MR spectra.     

Copper(II)-Catalyzed (3+2) Cycloaddition of 2H-Azirines to Six-Membered Cyclic Enols as a Route to Pyrrolo[3,2-c]quinolone,Chromeno[3,4-b]pyrrole,and Naphtho[1,8-ef]indole Scaffolds

A method for the [2+3] pyrroline annulation to the six-membered non-aromatic enols using 3-aryl-2H-azirines as annulation agents is developed in the current study. The reaction proceeds as a formal (3+2) cycloaddition via the N1-C2 azirine bond cleavage and is catalyzed by both Cu(II) and Cu(I) compounds. The new annulation method can be applied to prepare pyrrolo[3,2-c]quinoline, chromeno[3,4-b]pyrrole, and naphtho[1,8-ef]indole derivatives in good to excellent yields from enols of the quinolin-2-one, 2H-chromen-2-one, and 1H-phenalen-1-one series.     

Hydrazide-catalyzed 1,3-dipolar nitrone cycloadditions

The triflate salts of cyclic hydrazides function as asymmetric catalysts for the [3+2]cycloadditions of nitrones with α,β-unsaturated aldehydes. The camphor-derived hydrazides show a preference for the exo isomers during these reactions, providing a compliment to other organically catalyzed dipolar cycloadditions. Enantiomeric excesses as high as 93% were realized for the exo isomers, while some endo products were obtained in 94% ee.     

Regioselective synthesis of 5,6-polymethylene-3-cyanopyridine-2(1H)-thiones and fused heterocycles based on them

Condensation of 2-hydroxymethylenecyclopentan-1-one or -cyclooctan-1-one sodium salts with cyanothioacetamide afforded 5,6-polymethylene-3-cyanopyridine-2(1H)-thiones which were regioselectively alkylated at the sulfur atom by alkyl halides. Derivatives of 3-cyanopyridine-2(1H)-thione and 2-alkylthio-3-cyanopyridine were used for regioselective synthesis of substituted heterocycles: 3-aminothieno[2,3-b]pyridines, pyrido[2,3∶2′,3′]thieno[4,5-d]pyrimidines, and pyrido[2,3∶2′,3′]thieno[4,5-d]oxazines.     

A novel conversion of acetylenic 1,2,4-triazoles into 3-alkyl-5-arylpyridazines

Bromination of 2-aryl-1-[1,2,4]triazol-1-ylalk-3-yn-2-ols gives 6-bromo-7-hydroxy-5-alkyl-7-aryl-7,8-dihydro-[1,2,4]triazolo[1,2-a]pyridazin-4-ylium salts, which are converted by treatment with strong alkali into novel 3-alkyl-5-arylpyridazines.     

Low valent phosphorus in the molecular anions [P5Se12]5- and beta-[P6Se12]4-: phase change behavior and near infrared second harmonic generation

The caesium salts of the novel molecular anions [P5Se12]5- and [P6Se12]4- are phase change materials and exhibit near infrared, non-linear optical second harmonic generation; [P5Se12]5- is a coordination complex with an octahedral P3+ center chelated by two [P2Se6]4- ligands whereas [P6Se12]4- features a [P2]4+ dimer chelated by two [P2Se6]4- ligands.     

3-methylthio-1,2-dithiolylium salts : Reaction with 4-hydroxy-6-methyl-2H-pyran-2-one and 4-hydroxycoumarin

The reaction of 4- and 5-aryl-3-methylthio-1,2-dithiolylium iodides with 4-hydroxy-6-methyl-2$\text{H}$-pyran-2-one and 4-hydroxycoumarin has been studied. 4-Substituted salts yielded 3-aryl-7-methyl-2-thioxo-2$\text{H}$,5$\text{H}$-pyrano [3,2-c]pyran-5-ones and 3-aryl-2-thioxo-2H,5H-pyrano[3,2-c]benzo[e]pyran-5-ones, respectively, whereas 5-substituted salts gave rise to 3-(5′-aryl-1′,2′-dithiol-3′-ylidene)-6-methyl-2$\text{H}$-pyran-2,4-diones and 3-(5′-aryl-1′,2′-dithiol-3′-ylidene)-2$\text{H}$-benzo [b]-pyran-2,4-diones.     

Fast atom bombardment mass spectra of telluronium salts

The fast atom bombardment (FAB) mass spectra of telluronium salts were studied. The spectra exhibit the intact cation (C⁺) and cluster ions ([M + C]⁺). The principal fragment ions in the FAB mass spectra of telluronium salts are [RTe]⁺, [R₂Te]⁺˙, [R₂Te − H]⁺, [RTeR′]⁺˙, and [RTeR′ + H]⁺. When the anion was [BPh₄]⁻, interesting cluster ions such as [M + C − BPh₃]⁺ appeared.     

3 + 2] cycloaddition reactions of 4-alkyl-3-hydroxy-2H-pyrazolo[4,3-c]isoquinolinium inner salts

Heating dipolarophiles with 4-alkyl-3-hydroxy-2H-pyrazolo[4,3-c]isoquinolinium hydroxide inner salts results in [3 + 2] cycloaddition across positions 3a and 5 of the aromatic system to give the [3 + 2] cycloadducts in good yield. When the 4-alkyl substituent is a 2-acetate ester and the methylene group can be deprotonated, a second mode of [3 + 2] cycloaddition becomes available for the resulting anion (across the side chain methine group and position 5 of the aromatic system) and occurs under basic conditions, allowing either of two modes of [3 + 2] cycloaddition to be selected by appropriate choice of reaction conditions.     

Ethynyl carbonium ions. 3. Diene synthesis with 4-phenylethynylpyrylium salts

Norbornadiene derivatives of pyrylium salts were obtained for the first time by [4+2] cycloaddition of cyclopentadienes and 2,6-diaryl-4-phenylethynylpyrylium salts with and without methyl groups in the 3 and 5 positions. Their photochemical transformations were studied.See [1] for Communication 2.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 307–311, March, 1990.The authors thank M. I. Knyazhanskii for discussing the photochemical results.